The specific objectives of this research are: 1) to determine oncogene activations are involved in AIDS therapy induced mouse thymic lymphoma, 2) to determine if deletions in chromosome 4 are present in these lymphomas and 3) to determine if tumor suppressor gene expression occurs in these tumors. We will determine activated "ras" oncogene expression and allelic deletions in ddC induced thymic lymphomas. For this purpose B6C3F1 mice with intact ecotropic proviral sequences that can be activated, and NIH Swiss mice with truncated proviral sequences that cannot be expressed will be treated with ddC treatment for 6 months at a contract laboratory. Tymic lymphomas and related tumors caused by ddC treatment will be evaluated for "ras" oncogenes, tumor suppressor gene, and chromosome deletions in the Laboraories of the Environmental Carcinogenesis Program.